apache/cassandra · error · IllegalArgumentException

Cannot combine -dc and -hosts options.

Error message

Cannot combine -dc and -hosts options.

What it means

RepairOption.parse rejects repair requests that specify both datacenter and host restrictions. A repair is scoped either by datacenters or by explicit hosts, never both, so supplying both -dc and -hosts is treated as a contradictory request. IllegalArgumentException is thrown before the repair starts.

Source

Thrown at src/java/org/apache/cassandra/repair/messages/RepairOption.java:287

        if (cfStr != null)
        {
            Collection<String> columnFamilies = new HashSet<>();
            StringTokenizer tokenizer = new StringTokenizer(cfStr, ",");
            while (tokenizer.hasMoreTokens())
            {
                columnFamilies.add(tokenizer.nextToken().trim());
            }
            option.getColumnFamilies().addAll(columnFamilies);
        }

        // validate options
        if (jobThreads > MAX_JOB_THREADS)
        {
            throw new IllegalArgumentException("Too many job threads. Max is " + MAX_JOB_THREADS);
        }
        if (!dataCenters.isEmpty() && !hosts.isEmpty())
        {
            throw new IllegalArgumentException("Cannot combine -dc and -hosts options.");
        }
        if (primaryRange && ((!dataCenters.isEmpty() && !option.isInLocalDCOnly()) || !hosts.isEmpty()))
        {
            throw new IllegalArgumentException("You need to run primary range repair on all nodes in the cluster.");
        }
        if (pullRepair)
        {
            if (hosts.size() != 2)
            {
                throw new IllegalArgumentException("Pull repair can only be performed between two hosts. Please specify two hosts, one of which must be this host.");
            }
            else if (ranges.isEmpty())
            {
                throw new IllegalArgumentException("Token ranges must be specified when performing pull repair. Please specify at least one token range which both hosts have in common.");
            }
        }

        return option;

View on GitHub (pinned to 88fd0f6a0e)

Solutions

  1. Use only -hosts when targeting specific nodes
  2. Use only -dc when scoping the repair to whole datacenters
  3. Remove one of the two flags in your script/config

Example fix

// before
nodetool repair -dc dc1 -hosts 10.0.0.1 keyspace1
// after
nodetool repair -dc dc1 keyspace1
Defensive patterns

Strategy: validation

Validate before calling

if (dcList != null && !dcList.isEmpty() && hostList != null && !hostList.isEmpty())
    throw new IllegalArgumentException("Specify either -dc or -hosts for repair, not both");

Try / catch

try { RepairOption.parse(opts); } catch (IllegalArgumentException e) { if (e.getMessage().contains("Cannot combine -dc and -hosts")) { /* drop one scope and re-invoke */ } else throw e; }

Prevention

When it happens

Trigger: nodetool repair -dc dc1 -hosts 127.0.0.1 (or RepairOption.parse with options containing both DATACENTERS and HOSTS entries non-empty).

Common situations: Scripts accumulated flags over time; operators combining a DC filter with a specific endpoint to 'narrow further'; copy-paste from two different runbooks.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/c3d9faa1c9eff194. Report an issue: GitHub.